As is known in the art, with a vehicle equipped with a manual transmission, during a typical, driver-actuated gearshift event, the driver himself/herself matches the torque during the phases of the shift by adjusting the accelerator pedal position. The pedal position actuates either mechanically or electronically, the intake throttle valve.
As is also known in the art, with an Automatic Shift Manual (ASM) transmission the traditional manual gearshift lever is replaced with operator hand-operated up-shift and down-shift paddles which are part of a driver interface. The ASM transmission uses a sophisticated electromechanical control system to eliminate clutch pedal control by the operator of the vehicle completely. More particularly, with an ASM transmission, the driver makes gear selections with the easy-to-operate electronic paddles while the vehicle's control system executes the driver's decision. During such execution, the system co-ordinates all gear-change events including engine torque ramp-down and ramp-up. Thus, an ASM transmission is an automatic manual gearbox because the mechanical linkages, which would commonly be controlled by the operator of the vehicle in a manual transmission, are supplanted by high-speed electrohydraulic actuators.
There are two operator selectable modes by which an ASM transmission can operate: (1) An Operator Select-ASM (OS-ASM) mode; and (2) an Automatic Select-ASM (AS-ASM). The particular mode is selected by the operator by pressing one of a pair of operator hand-operated buttons which are also part of the driver interface. In the OS-ASM mode the operator depresses the appropriate up-shift or downshift paddle to indicate a desire for a gear shift; in the AS-ASM mode the demand for a gearshift is not under the operator's control but rather under control of the system itself. For example, in the AS-ASM mode, the demand for a gearshift is produced by an engine control unit and is computed as a function of driver demanded torque and engine operating conditions.
In the prior art, the ASM gearshift event is performed analogously to that of a manual transmission except that the engine control unit aboard the vehicle controls the intake throttle valve position and spark timing. A gearshift as a function of time, according to the prior art, is shown in FIG. 1. The control mode is shown along the top. During pre-shift, the engine is controlled by a pedal follower mode wherein engine parameters are controlled by an engine control unit (ECU) based on input signals fed to such ECU such as accelerator pedal position, current engine operating conditions, temperature, pressures, and others. During the subsequent gearshift event, the engine is controlled based on torque requests from a transmission control unit (TCU) coupled to the transmission. In Phase I of the gearshift event, engine torque is reduced and the clutch is opened to disengage the engine from the transmission. In Phase II, engine torque is at a minimum because the engine is decoupled from the transmission; thus, there is no driveline load on the engine. Further, during Phase II, the gears are changed from an initial gear to a final gear, eg., 1st gear to 2nd gear. During Phase III, the clutch is closed to re-engage the engine with the transmission and engine torque is restored.
Continuing to refer to FIG. 1, an operator demanded torque is shown in the engine torque portion of the graph. The shift shown in FIG. 1 is an upshift in which the relative ratio of the transmission output shaft speed to engine speed increases in going from the initial to final gear. Typically, but not necessarily, the operator is demanding increased engine torque in such an upshift event as shown. However, during the gearshift, the engine is disengaged from the transmission; thus, the engine is temporarily unable to provide operator demanded torque. As mentioned above, the transmission control unit becomes the torque requester from the engine via the engine control unit, i.e., TCU transmits request to ECU; ECU commands engine to provide, or attempt to provide, as the case may be, the transmission requested torque. During Phase I, the transmission requests a downward torque trajectory (i.e., a reduction in torque). Initially, the engine is able to provide the decreasing torque by retarding spark timing. However, the authority over torque provided by spark timing is insufficient to achieve the required torque reduction. Thus, shortly into Phase I, the transmission requested and actual engine torques deviate one from the other. This leads to an undesirable speed flare. The other measure undertaken during Phase I to cause a torque reduction is for the throttle valve to be closed. The control signal driving the throttle valve is based on an error signal generated from the difference between the transmission requested and actual engine torques.
In the throttle position/airflow portion of the FIG. 1, it can be seen that the throttle valve is commanded to gradually close shortly after the start of the gearshift event. The throttle valve has the effect of reducing airflow to the engine. However, unlike spark timing, which is a fast actuator in which the effect of making the change occurs in the next engine firing, the effect of reducing airflow is delayed from the throttle valve actuation. There is a slight actuator delay due to physical limitations of moving the throttle valve, i.e., there is a delay from the time that the signal is received by the throttle valve actuator and the throttle valve assumed the commanded position. A more significant delay is the manifold emptying delay that delays the change in airflow. Thus, in Phase I of FIG. 1, airflow lags throttle valve position changes. Thus, in the engine torque portion of FIG. 1, the actual decrease in engine torque lags the transmission requested torque decrease during Phase I.
Continuing with FIG. 1, the transmission requests a sudden decrease in torque when the clutch is fully open, shown as time to in FIG. 1. It would be desirable to enter into Phase II at time to. However, the actual torque exceeds transmission requested torque by more than a tolerable margin. Thus, the time between time to and the start of Phase II is a delay portion, waiting for the engine torque, and thus engine speed, to reduce to a tolerable difference. This tolerable difference between actual and transmission requested torque is shown as □ in FIG. 1. When the actual engine speed is close enough to transmission desired engine speed to allow gear changing to occur and the gearshift event begins Phase II, in which the gear changing occurs.
Continuing to refer to FIG. 1, when the transmission has completed the gear change of Phase II, which includes gear selection and synchronization, the transmission requests a jump in torque which the engine cannot immediately fulfill. Thus, actual torque goes from being a little higher, by □, than requested torque in Phase II, to being less than transmission requested torque in Phase III. Immediately, the throttle is commanded to adjust toward a more open position at the beginning of Phase III. However, the throttle valve is adjusted based on error in transmission requested torque and actual torque. Furthermore, there are both and actuator delay, i.e., a delay from the time that the throttle is commanded to open and when it opens, and an aerodynamic delay, i.e., a manifold filling delay in which the intake manifold takes time to attain the new requested pressure and a delay due to the air accelerating to the new airflow condition. Because the adjustment is based on the present error and the transmission requested torque is rising monotonically throughout Phase III, airflow fails to catch up causing the difference between transmission requested torque and actual torque to be different throughout Phase III. At the end of Phase III, as shown in FIG. 1, there is a torque mismatch between the actual torque and transmission requested torque. The clutch is fully closed and the torque mismatch causes engine speed to falter. A short time into the post-shift phase, actual torque catches up to operator demanded torque.
In an alternative situation, not shown in FIG. 1, the end of Phase III is delayed until actual torque achieves the level of operator demanded torque. Specifically, this means that the closing of the clutch is delayed such that clutch closing coincides with the time when actual torque first achieves operator demanded torque.
In the scenario shown in FIG. 1, the operator feels a drop in engine speed and a sluggish feel in the initial portion of the post-shift phase. In the alternate scenario, Phase III is a protracted period, also giving the operator a slow shift sensation. Both scenarios provide the driver with a sluggish shift feel.